A starting BV cannot carry back its initial losses because it does not have any profit history. In case of a sole proprietorship or a partnership the private entrepreneur can carry back its losses to any positive private (wage) income of the past 3 years. Moreover, in a BV a certain market wage is taxed to its main directors/shareholders (sometimes even if the BV is not yet profitable). Based on the above, it is usually better to postpone the BV for a couple of years and to migrate into a BV tax-free when profits exceed say € 150,000.
In some cases a BV can otherwise be necessary (limitation of liability, venture capital participation, franchising conditions etc.). In these cases we can investigate if we can combine a BV with a sole proprietorship to achieve the best of both worlds.
Please contact me, if you have any question about your case.